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An incursion into the sensory world of plants

What do plants perceive of the world surrounding them and how do they react to it? What tells them when it’s time to flower? Every bit of information they need is right there, all around them…

Day and night, or plant-version “vision”

Light provides information that is essential to plant survival and reproduction. In addition to allowing plants to produce sugars, light controls thousands of reactions at the heart of their cells.

Photoreceptors are found primarily in the leaves as well as at the ends of stems, in the zone of elongation. They detect not only changes in light that the human eye cannot discern but also the direction of the light. They act like switches that manage, activate and deactivate some of the plant’s internal reactions. They play a very important role in triggering flower production.

The alternation of day and night (more precisely the duration of each of those periods) along with the temperature “inform” the plant about the growing season and conditions.

It’s in the air

The messages conveyed by the air are of different types. A well-known example is the ripening of fruit provoked by ethylene. The more fruit there is maturing, the greater the concentration of ethylene, which has a domino ripening effect on fruit located close by. Animals, attracted by the perfume of ripe fruit, will eat that fruit and scatter the seeds in their feces.

A tree whose leaves get nibbled on by caterpillars releases molecules that “inform” neighboring trees that a pest is at work and that they must defend themselves.

Physical contact

A plant’s contact with the rain, an animal, the wind or an object can give rise to various reactions. The Venus fly trap, that insectivorous plant with the formidable snare, reacts to the presence of insects on its leaves by closing in 1/10th of a second. Mimosa leaves fold inward at the slightest touch. In certain cases, repeated contact can induce a form of stress that will check or halt growth. Think of trees growing on windswept cliffs: they develop fewer branches, and a stockier trunk.

Thanks to their ability to hear, animals can communicate quickly among themselves. This comes in very handy when a predator is in sight. For immobile beings, hearing a predator (or a grazing animal) coming is not very useful...

Whatever some people might have to say about it, plants have been evolving on Earth for hundreds of thousands of years and seem “deaf” to surrounding sounds.

Plants interact with their environment by way of a silent dialogue consisting of signals. Watch them at work!